Mercury has many useful applications in industry. However, its toxic nature can create serious problems when this element is released to the environment, e.g., to landfills, soil, sand, gravel, building materials, and the like.
One particularly effective method for the extraction of mercury from contaminated solid materials is described in U.S. Pat. No. 5,226,545. The method involves treatment of contaiminated solid material, e.g., phenolic plastic parts, with a liquid oxidant-complexing agent composition which oxidizes the mercury to form which can be solubilized by the complexing agent. The mercury-containing liquid phase is then separated from the solid material. It can be further treated to regenerate the oxidant-complexing agent composition and convert soluble mercury to recoverable elemental mercury. A preferred oxidizing agent is iodine, while a preferred complexing agent is a water-soluble halide salt such as potassium iodide.
While the process described above is effective in extracting mercury, it can be commercially expensive. This is in large part due the loss of expensive oxidizing agents and complexing agents, such as iodine and iodine salts, during the process. The iodine-based materials are very soluble in organic materials such as phenolic plastics, and can be absorbed by the plastics during the decontamination process. Once absorbed, the iodine is unrecoverable, thereby decreasing the commercial feasibility of the overall process. Rinsing the treated solution with water (and preferably, at elevated temperature) sometimes results in the recovery of a portion of the lost iodine, but substantial amounts remain unaccounted for.
Some methods for the recovery of iodine are known in the art. For example, U.S. Pat. No. 4,131,645 describes a process to recover iodine from brine, through the use of a basic anion exchange resin. In an article by N. R. Dhar, a technique is described in which sodium formate is reacted with iodine, forming iodide salts which have very little affinity for organic resin solids [(J. Chem. Soc. (London), 111 (1917) 726].
There is still a great deal of interest in an effective, practical process of maximizing the recovery of iodine from an environment, e.g., from a mixture which had been previously treated with at least one iodine-based compound. Furthermore, the process should be compatible with related processes being carried out at the same site, such as a mercury remediation. The process should also permit the recycling of iodine-based reagents for further use.